Feed device for feeding molten metal in to a crystallizer

ABSTRACT

A drop feeder ( 1 ) for feeding molten metal into an ingot mould ( 15 ) comprises a distributor ( 3 ) having a substantially prismatic shape, with one of the faces open, in which the inside of the distributor comprises three tanks ( 4, 5, 6 ), separated by walls ( 7, 8 ) functioning as weir for the molten melt poured into the intermediate tank ( 5 ). There are provided slots ( 10 ) arranged on the faces of the distributor ( 3 ) for emptying of the molten metal from the distributor into the ingot mould or into a second distributor.

FIELD OF THE INVENTION

The invention relates to a device for discharging metal in the moltenstate from a container, for example from a casting ladle or a tundish,into an ingot mould of a continuous-casting line with rolls.

PRIOR ART

Normally, in continuous-casting plants, the metal arriving, in themolten state, for example from an electrical furnace, or else from aconverter is made to undergo a series of operations of transfer betweencontainers before being cast into the ingot mould in order to guaranteeoptimal conditions in the ingot mould so as to ensure a quality casting.

Particular problems arise in the continuous casting of metal strip usingcounter-rotating rolls. In this case, the steel coming out of theproduction furnace is collected in a casting ladle, from which it isdischarged into one or more tundishes, each of which supply one or morebasins of molten metal above two cooled counter-rotating crystallizerrolls, which form the ingot mould and in which the metal solidifies,coming out in the form of finished product.

It is known that the quality of the end product, and also the verycarrying-out of the process can be jeopardized by the situation thatarises in the ingot mould and in particular by the shape and by thefluid-dynamic situation of the metal in this area. In fact, in atwo-roll continuous-casting machine, there is the need to form in theingot mould, which consists of a substantially V-shaped vessel definedby the space between the two rolls, a meniscus of liquid metal, which ispossibly uniform, homogeneous, and flat throughout the axial extensionof the rolls. A uniform distribution of the liquid steel in thecrystallizer and, consequently, a uniform solidification, on the onehand prevents the formation of cracks during casting, and on the otherguarantees non-uniform solidification and prevents trapping ofimpurities, which lie at the origin of cracks in the course of thesubsequent processing operations. Furthermore, the level of the liquidsteel in the distributor must be such as to prevent formation ofvortices on the meniscus, In so far as this would bring about trapping,in the solidified steel strip, of impurities that are present in theliquid steel and float on the meniscus. Such an eventuality would bringabout the onset of defects such as cracks, surface defects, etc. thatcould be accentuated in the course of the subsequent processingoperations that the product has to undergo, for example, rolling,forming, etc.

Discharge devices of the known art that have been designed to addressthe above problems are of a complex shape and are difficult to build, inaddition to involving the need for considerable maintenance operations.Uniformity of distribution has also been achieved with the use of anumber of containers arranged in series, in order to reduce in this waythe speed at which the liquid steel is fed. This solution, however,complicates the casting plant. Consequently, there is felt the need tohave available discharge devices which will at the same time be easy tobuild and will contribute to a uniform outflow of the liquid metal, soguaranteeing formation and maintenance of a uniform meniscus in theingot mould in order to obtain an end product that is free from defects.

SUMMARY OF THE INVENTION

It is hence a purpose of the present invention to furnish a remedy tothe problems referred to above by providing a device for feeding moltenmetal starting from a container, for example a tundish, which willproduce a flow of molten metal into the ingot mould that is free fromany turbulence for formation of a meniscus that is as uniform aspossible.

A further purpose is to provide a feed device having an alternativeshape that will have a simple design and will prevent need for use of anumber of containers arranged in series along the casting flow in orderto reduce the speed of inflow of the liquid steel.

The problems set forth above have been solved in accordance with themain claim by means of a drop feed device for supplying an ingot mouldwith molten metal, comprising a distributor having a substantiallyprismatic shape, with one of the faces open, in which the inside of thedistributor comprises at least three tanks, of which two first tanks arearranged at the ends of the distributor and at least one further tank isset in an intermediate position with respect to the first two tanks, inwhich the further intermediate tank is separated from the first twotanks by respective separating walls, the dimensions of which are suchas to cause one of their edges to perform a function of weir for passageof the molten metal between said intermediate tank, when it is full, andsaid two first tanks, in which there are provided holes arranged on oneor more faces of the distributor in such a position and of suchdimensions and shape as to be able to perform a function of emptying themolten metal from said two first tanks towards the outside of thedistributor before reaching a level equal to that of the edge of each ofthe separating walls which perform the function of weir.

Thanks to the particularly simple and compact shape of the feed devicethat comprises an intermediate distributor downstream of the dischargerand thanks to the arrangement of the tanks that make up saiddistributor, a homogeneous flow of liquid steel is generated duringdischarge.

The task of the first tank is to reduce the kinetic energy of the liquidsteel pouring from the tundish. Also the arrangement and shape of theside slots guarantee a sufficient rate to maintain the speed of castingaccording to design.

A further improvement of the flow is obtained by means of a feed devicethat comprises also the use of a main distributor downstream of theintermediate distributor. In this way, the flow of steel that is pouredinto the ingot mould can further be rendered uniform and homogeneous.The result is thus a meniscus without any swirling motion that ensuresthe production of a casting product of higher quality.

LIST OF FIGURES

Further advantages that may be achieved with the present invention willemerge more clearly to the person skilled in the sector from the ensuingdetailed description of a non-limiting example of a particularembodiment of the discharge device, with reference to the followingfigures, in which:

FIG. 1 shows a cross section according to the vertical plane of castingof a continuous-casting machine that comprises the feed device accordingto the invention;

FIG. 2 shows a cross section according to the vertical plane of traceA-A of the casting machine of FIG. 1;

FIG. 3 shows a cross section according to the vertical plane of castingof a feed device according to the invention; and

FIG. 4 shows a cross section according to the vertical plane of traceB-B of the feed device of FIG. 3.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

With reference to the figures, described herein is an embodiment of afeed device for feeding molten metal, in particular liquid steel, intoan ingot mould for a continuous-casting machine with two crystallizerrolls. In particular, FIG. 1 shows a cross section according to avertical plane parallel to the axis of the crystallizer rolls of partsof a continuous-casting machine, designated, as a whole, by thereference number 1, comprising the feed device according to theinvention. In the remainder of the description, reference will be madeto steel, but it is understood that the device can be adapted to thedischarge of other metals for which the same casting technique is used.

The molten steel coming from a tundish, not represented in the figures,is poured, through a discharger 2, into a first distributor 3. Thedischarger 2 is substantially shaped like a funnel turned upside-downwith the divergent section set downwards in the direction of thedistributor 3, and has a section orthogonal to its axis that iscircular. Alternatively, the cross section is circular in the topportion of the discharger and has a rectangular development towards itsbottom portion, the various sections being appropriately radiused alongthe axial development of the discharger 2. The angle of divergence ofthe internal walls is less than 70°.

This arrangement of the discharger 2 produces the advantage of reducingthe speed of fall of the liquid steel when it arrives in thedistributor. Furthermore, the pattern of the various sections and theangle of divergence are chosen in such a way that any detachment fromthe internal wall of the discharger 2 is prevented.

The first distributor 3, illustrated in greater detail in FIGS. 3 and 4,is a container open in the top part and having a rectangular shape inplan view, with the longer part set along the axis parallel to thedirectrices of the rolls. The first distributor 3 is divided on theinside, along its longer dimension, into a number of tanks, which in theembodiment illustrated in the figures are three, but which in otherembodiments may be of a larger number. The discharger pours the steelinto the central tank 5, delimited by two walls 7, 8, which separate It,respectively, from the end tanks 4 and 6. The separation walls 7, 8 arelower than the external perimetral walls of the central tank 3, so that,with their respective top edges 7′, 8′, they are able to perform afunction of weir for the molten steel poured from the discharger 2. Inoperation, when the central tank 5 is filled with steel, the flow afterthe impact with the bottom of the central tank 5 follows a pattern thatenables overflow beyond the weir walls 7 and 8, thus losing a major partof its kinetic energy, and subsequently flows into the end tanks 4 and6, where there is a further stage of reduction of the kinetic energy ofthe steel, which reaches a more tranquil state. The pattern of the flowbetween the central tank 5 and the end tanks 4 and 6 is indicatedschematically by the flow lines 9, 9′. The walls 7, 8 may have a heightfrom the bottom of the central tank ranging preferably from 10 mm to 70mm, according to the casting requirements, for example, the speed ofcasting and the dimensions of the steel strip to be produced.

From the end tanks 4 and 6, the liquid steel 11 flows, through series ofslots 10 arranged in the bottom part of the side walls of the tanks 4,6, into a second distributor 12, of a known form and hence not furtherdescribed herein, from which there is performed discharge into the ingotmould formed by the space comprised between the counter-rotatingcrystallizer rolls 13, 13′. The number, shape, and dimensions of theslots 10 vary both according to the metal to be molten and according tothe speed of outflow necessary in the casting machine. The dischargeslots 10 can be arranged in various positions on the external walls ofthe end tanks 4 and 6, as likewise on the external end walls of thedistributor 3. They are appropriately distributed so as to ensure auniform, homogeneous, and non-turbulent distribution of the steel.

Advantageously, the distributor 3 has all its side faces inclined so asto be convergent, or alternatively, just some of the walls areconvergent, and in this case a variant distributor is obtained, whichpresents a combination with some vertical walls.

Whenever envisaged, the second distributor 12 in operation is generallyset Immersed in the ingot mould 15. Then, the steel strip of indefinitelength is produced from the ingot mould via the continuous-castingprocess, in a known way.

According to a second advantageous variant of the invention, the steelflows from the first distributor 3, through the slots 10, directly intothe ingot mould 15, without the presence of the second distributor 12.

According to a further advantageous variant of the feed device of theinvention, the central tank 5 has a depth smaller than that of the endtanks 4 and 6, and this is obtained, for example, by locating the bottom14 of the tank in a position that is set in with respect to the endtanks 4 and 6.

1. A drop feed device (1), for a two-roll continuous strip castingmachine, for feeding one ingot mould (15) with molten metal, comprisinga distributor (3), having a substantially prismatic shape with one ofthe faces open and having a rectangular shape in plan view, with holes(10) arranged on one or more side walls of the distributor (3)characterized in that the inside of the distributor (3) comprises atleast three tanks (4, 5, 6), arranged along its longer dimension whereintwo first tanks (4, 6) are arranged at the end of the distributor (3)and at least one further tank (5) Is set in an Intermediate positionwith respect to the two first tanks (4, 6), in which the furtherintermediate tank (5) is separated from the two first tanks (4, 6) byrespective separating walls (7, 8), whose the dimensions are such as tocause their edges (7′, 8′) to perform a function of weir for passage ofthe molten metal between said Intermediate tank (5), when it is full,and said two first tanks (4, 6), and in that the holes (10) are arrangedin such a position and are of such dimensions and shape as to be able toperform a function of emptying the molten metal from said two firsttanks (4, 6) towards the outside of the distributor (3) before reachinga level equal to that of the edges (7′, 8′) of the separating walls (7,8).
 2. The drop feed device according to claim 1, wherein the holes (10)are substantially elongated having the shape of a slot.
 3. The drop feeddevice according to claim 1, wherein a further distributor (12) isprovided having an elongated, substantially prismatic shape, designed tobe set between said distributor (3) and an ingot mould (15).
 4. The dropfeed device according to claim 3, wherein a discharger (2) is provided,which is designed to discharge molten metal from a tundish or othercontainer into the Intermediate tank of the distributor (3).
 5. Thedevice according to claim 4, wherein the discharger (2) has asubstantially funnel-like shape, and the angle of divergence of theinternal walls of the discharger is less than 7°.
 6. The deviceaccording to claim 1, wherein some or all of the faces of thedistributor (3) are mutually convergent.